1. Field of the Invention
The present invention relates to injection compression molding, particularly to gate sealing and prevention of occurrence of vertical burs at the time of gate cutting.
2. Description of the Prior Art
Generally, in an injection compression molding (referred hereafter to as "compression molding"), as shown in FIG. 3, molding material is filled in a cavity 3 formed by abutting a mold 2 against a stationary mold 1, and a male cutter 6 is made to advance toward a female cutter 5 to seal a gate and at the same time to pierce the center of the cavity i.e. (cutting the gate), then the filled material is kept under a compressed state and solidified while being cooled.
In such a compression molding, in order to obtain moldings in high precision, it is important for the material to be pressed rapidly before cooling and solidification. However, if the pressing of the material starts before finishing the gate sealing, the material resin leaks by backward flow out of a gate portion 5a of the female cutter 5 and a sufficient pressing of the material cannot be given resulting in insufficient copy from the molds. Because of that reason, in the conventional molding in practise, the male cutter 6 is arranged to carry out its forwarding movement at a constant and such swift speed as rapid as possible after the finishing of filling the material into the cavity 3, in order to carry out the gate sealing at such a timing as soon as possible.
However, in that conventional method, in order to carry out the gate sealing rapidly, when making the male cutter move forward at a constantly rapid speed, the material located at the portion adjacent to a gate portion 5a of a female cutter is dragged in, so that a so-called vertical bur which may arise in the direction of forwarding movement of the male cutter is apt to occur, which has caused to make a trouble in molding. And, as shown in FIG. 4, in the case where such an optical disc as represented by a compact disc D is molded as a product, if there is a vertical bur B of the disc around the opening (cut portion) C located at the center of the disc, it may cause a trouble in the engagement with a turn table T of a player.